Long Term Evolution (LTE) is the fourth-generation mobile communication technologies standard developed within the 3rd Generation Partnership Project (3GPP) to improve the Universal Mobile Telecommunication System (UMTS) standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. The Universal Terrestrial Radio Access Network (UTRAN) is the Radio Access Network (RAN) of a UMTS and Evolved UTRAN (E-UTRAN) is the RAN of an LTE system. In an E-UTRAN, a User Equipment (UE) is wirelessly connected to a Radio Base Station (RBS) commonly referred to as an evolved NodeB (eNodeB or eNB) in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to a UE and receiving signals transmitted by a UE.
FIG. 1 illustrates a conventional RAN in an LTE system. An eNodeB 101 serves a UE 103 located within the eNodeB's geographical area of service also called a cell. The eNodeB 101 manages the radio resources in its cell and is directly connected to a Core Network (CN) node 105.
Conventionally, an LTE RAN is operated by an operator over a licensed frequency band. Lately, it has been proposed to run LTE RAN also over unlicensed frequency bands by aggregating licensed and unlicensed frequency bands. The use of the unlicensed frequency band is made possible by applying a listen-before-talk (LBT) mechanism, which means that a subframe can be scheduled for data transmission on a radio channel only when the unlicensed frequency band carrier is determined to be idle. In this way, a fair competition is allowed between LTE and other wireless radio systems such as WiFi, with regards to the use of the unlicensed frequency band. For the LTE RAN, the solution implies that a primary carrier is configured on the licensed frequency band while the unlicensed frequency band shall only be used for a secondary carrier. This can be referred to as licensed carrier assisted LTE-Unlicensed (LTE-U), or License Assisted Access LAA. The object of such a carrier aggregation solution is to make it possible for an operator to make use of an unlicensed frequency band having relatively low load and thereby increase the utilization of such an unlicensed frequency band. It may be expected that the licensed carrier assisted LTE-U system is mainly designed for LTE operators as a licensed carrier is mandatory.
A Home eNodeB (HeNB), also referred to as a Femto base station, has already been standardized in 3GPP. FIG. 2a illustrates a typical scenario of a HeNB deployment, and FIG. 2b represents an LTE network structure used with the HeNB, in which a HeNB gateway (HeNB GW) and a HeNB management system are introduced into the operator's network. Some limitations related to the HeNB are the following:                HeNB runs in a licensed frequency band. This means that it is controlled by the operator that owns the frequency band and mainly serves subscribers of this operator.        HeNB is not cost-efficient with regards to charging from an end-user perspective. At home or in office, a subscriber may like to select a fixed broadband operator to achieve a data service as cost efficient as possible.        
There are solutions to share HeNB between multiple operators, e.g. disclosed in WO2012/085829. According to one method, the HeNB tries to setup an internet security (IPsec) protocol tunnel when the HeNB receives the Public Land Mobile Network (PLMN) identity from the UE. The IPsec protocol tunnel is associated with the S1 and Iu interfaces that are associated with the HeNB GW of the PLMN. The HeNB then communicates between the UE and the PLMN via the IPsec protocol tunnel. However, it is still a fact that the HeNB may only be deployed by an operator, or by other operators with the permission from the corresponding operator. Furthermore, the solution for HeNB sharing between multiple operators is determined by these operators only and not by the subscribers.
Due to the limitations of the HeNB, the market situation of the HeNB is weak compared to the WiFi solution which has grown popular and therefore dominate the wireless local access market. With a WiFi solution for local access, a subscribed fixed broadband access is used for the connection. Advantages of WiFi are that a WiFi solution may be customized, the data cost may be low, and the manufacturing price may be low.
A standalone LTE RAN using an unlicensed frequency band only, i.e. without licensed carrier assistance, may be a promising future solution. An advantage of a standalone LTE RAN is that it makes it possible for anyone to deploy such a network and not only LTE operators. Other parties such as enterprises, building owners, and individuals may thus deploy an LTE RAN access point, similar to what is possible with a WiFi network today. Furthermore, a standalone LTE RAN using only an unlicensed frequency band may provide even better flexibility and user experience compared to WiFi.